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/* $Id: dma.c,v 1.1 1999/04/26 05:58:29 tb Exp $
* linux/kernel/dma.c: A DMA channel allocator. Inspired by linux/kernel/irq.c.
*
* Written by Hennus Bergman, 1992.
*
* 1994/12/26: Changes by Alex Nash to fix a minor bug in /proc/dma.
* In the previous version the reported device could end up being wrong,
* if a device requested a DMA channel that was already in use.
* [It also happened to remove the sizeof(char *) == sizeof(int)
* assumption introduced because of those /proc/dma patches. -- Hennus]
*/
#include <linux/kernel.h>
#include <linux/errno.h>
#include <asm/dma.h>
#include <asm/system.h>
/* A note on resource allocation:
*
* All drivers needing DMA channels, should allocate and release them
* through the public routines `request_dma()' and `free_dma()'.
*
* In order to avoid problems, all processes should allocate resources in
* the same sequence and release them in the reverse order.
*
* So, when allocating DMAs and IRQs, first allocate the IRQ, then the DMA.
* When releasing them, first release the DMA, then release the IRQ.
* If you don't, you may cause allocation requests to fail unnecessarily.
* This doesn't really matter now, but it will once we get real semaphores
* in the kernel.
*/
/* Channel n is busy iff dma_chan_busy[n].lock != 0.
* DMA0 used to be reserved for DRAM refresh, but apparently not any more...
* DMA4 is reserved for cascading.
*/
struct dma_chan {
int lock;
const char *device_id;
};
static struct dma_chan dma_chan_busy[MAX_DMA_CHANNELS] = {
{ 0, 0 },
{ 0, 0 },
{ 0, 0 },
{ 0, 0 },
{ 1, "cascade" },
{ 0, 0 },
{ 0, 0 },
{ 0, 0 }
};
int get_dma_list(char *buf)
{
int i, len = 0;
for (i = 0 ; i < MAX_DMA_CHANNELS ; i++) {
if (dma_chan_busy[i].lock) {
len += sprintf(buf+len, "%2d: %s\n",
i,
dma_chan_busy[i].device_id);
}
}
return len;
} /* get_dma_list */
int request_dma(unsigned int dmanr, const char * device_id)
{
if (dmanr >= MAX_DMA_CHANNELS)
return -EINVAL;
if (xchg(&dma_chan_busy[dmanr].lock, 1) != 0)
return -EBUSY;
dma_chan_busy[dmanr].device_id = device_id;
/* old flag was 0, now contains 1 to indicate busy */
return 0;
} /* request_dma */
void free_dma(unsigned int dmanr)
{
if (dmanr >= MAX_DMA_CHANNELS) {
printk("Trying to free DMA%d\n", dmanr);
return;
}
if (xchg(&dma_chan_busy[dmanr].lock, 0) == 0) {
printk("Trying to free free DMA%d\n", dmanr);
return;
}
} /* free_dma */
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